The invention disclosed herein may have been produced as a result of work performed under a project funded, in part, by one of the following federal agencies: NASA, NSF, and NIH. As a result, the U.S. Government may have rights to the invention claimed herein. The assignee hereof filed a patent application (Ser. No. 09/223,689) on behalf of the Applicant of the instant patent application, on Dec. 30, 1998 entitled Remote Magneto-elastic Analyte, Viscosity and Temperature Sensing Apparatus and Associated Methods of Sensing. The invention disclosed in both this patent application and the earlier-filed pending patent application (Ser. No. 09/223,689) were invented by Applicant hereof while employed by the assignee.
In general, the present invention relates to telemetry of environmental conditions using sensing devices remotely located from associated pick-up/receiver and processing units for chemical analyte and temperature sensing and monitoring. More particularly, the invention relates to a novel remote radio-frequency (RF) resonant-circuit sensing structure having a structural element made of a material that selectively responds to the analyte or surrounding temperature and associated new sensing apparatus and method of sensing. This novel sensing structure may be used to sense the presence, concentration, or absence of chemical elements and compounds (whether useful or unwanted/contaminating in a liquid, gas, or plasma state), pH levels, germs (bacteria, virus, etc.), enzymes, antibodies, and so on in a number of environments such as biomedical applications (whether in vivo or in vitro), within medical test samples, food quality/inspection (whether measuring moisture within sealed packing or outside of packaging), monitoring of heavy metals found in water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring of solid or gas manufacturing waste, etc. This new, versatile sensing apparatus and method provides information utilizing a unique remote resonant-circuit recognition technique and sensing structure, whether using one or several such structures positioned within a test environment to provide an array of information.
Known chemical sensing technologies generally require the operation of complex, specifically tailored sensing units, electrically connected, to monitor a target analyte. For example, Groger et al. has a FIG. 4 with a chemically sensitive film 93 positioned between coils 92 and 94 (each of which has been wrapped around a ferrite core); a FIG. 5 with eddy current probes 21 formed by chemical deposition or chemically etching a copper clad printed circuit board (PCB) substrate 11 of a conductive polymer film of polypyrrole, polythiophene or polyaniline which may be deposited directly onto the inductor array or separated by spacers; and a FIG. 6 showing a spiral-wound inductor eddy current probe 13 with a thick film ferrite core 42 deposited on (or etched on) a PCB substrate 12. The Groger et al. probe design is incorporated into an instrument that has a digital signal processor (D)DS) circuit. FIG. 9 illustrates that the probe 83 (such as that in FIGS. 3 or 6) is in electrical connection with, and driven by, sinewave generator 80, preferably a direct digital signal generator, and an op amp 85 to produce a waveform output 86.
Kaiser illustrates a sensor 12, measurement circuit 10 and responder unit 16 coupled to a PCB 22 as an integrated circuit 24 (see FIGS. 1, 2A, and 2B), all contained in a housing 18. The integrated circuit 24 (FIG. 2A) is electrically connected to a sensor electrode 20 and reference electrode 21. The potential difference that develops between the electrodes 20 and 21 in relation to ion concentration, is measured to provide a pH level reading. In FIG. 2B, the sensor 12 of integrated circuit assembly 24 is a temperature sensor which is completely sealed within housing 18. FIGS. 3, 4, and 5 illustrate measurement circuit 10 embodiments: In 3 and 4, a voltage follower 44 outputs a signal proportional to the potential difference detected at sensor 12; FIG. 5 illustrates a familiar Wheatstone bridge with an AC generator 200 powered by an interrogation signal sent by interrogation unit 14. In operation (FIGS. 1 and 6), the RP transmitting and receiving circuitry 64 of interrogation unit 14, transmits an inquiry signal. Sometime thereafter, upon detecting its proper responder unit address, the responder unit 16 transmits data from the measurement circuit 10 back to interrogation unit circuitry 64.
Lewis et al. describes an analog of the mammalian olfactory system (i.e., electronic-nose) having chemiresistor elements micro-fabricated onto a micro-chip. Each sensor has at least first and second conductive leads electrically coupled to and separated by a chemically sensitive resistor (FIG. 4A-1). Each resistor has a plurality of alternating nonconductive and conductive regions transverse to the electrical path between the conductive leads. The chemiresistors are fabricated by blending a conductive material with a nonconductive organic polymer such that the electrically conductive path between the leads coupled to the resistor is interrupted by gaps of non-conductive organic polymer material. See, column 3, lines 38-50. Lewis et al. describes this as xe2x80x9celectronic noses, for detecting the presence of an analyte in a fluidxe2x80x9d (col. 8). An electronic smelling system according to Lewis et al. (col. 7) has sensor arrays in electrical communication with a measuring device for detecting resistance across each chemiresistor, a computer, a data structure of sensor array response profiles, and a comparison algorithm.
The applicant hereof, in conjunction with others, developed a magneto-chemical sensor comprised of a thin polymeric spacer layer made so that it swells in the presence of certain stimuli, bounded on each side by a magnetically soft thin film, as described in an article co-authored by the applicant entitled A Remotely Interrogatable Magnetochemical pH Sensor, IEEE TRANSACTIONS ON MAGNETICS, VOL. 33, No. 5, SEPTEMBER 1997. When placed within a sinusoidal magnetic field the sensor generates a series of voltage spikes in suitably located detecting coils. The magnetic switching characteristics of the sensor are dependent upon the thickness of the sandwiched intervening polymeric spacer layer. The sandwiched xe2x80x9cchemical transduction elementxe2x80x9d of this magnetism-based technology was made of a lightly crosslinked polymer designed to swell or shrink with changes in the concentration of the species to be sensed. The magnitude of each of the voltage spikes generated by the sensor is dependent upon how much the sandwiched spacer layer has swollen in response to the given stimuli. This sensor can be used with interrogation and detection electronics commonly used in magnetic anti-theft identification marker systems.
In a subsequent structurally-modified magnetochemical sensor developed by the applicants hereof, with others (A Remotely Interrogatable Sensor for Chemical Monitoring, IEEE TRANSACTIONS ON MAGNETICS, VOL. 34, No.4, JULY 1998), a thin film single or array of magnetostatically coupled magnetically soft ferromagnetic thin film structure(s) is adhered to a thin polymeric layer made so that it swells or shrinks in response to a chemical analyte. The sensor is placed within a sinusoidal magnetic field and the magnetization vector of the magnetically soft coupled sensor structures periodically reverses direction generating a magnetic flux that can be remotely detected as a series of voltage spikes in pick-up coils. The four-square array is of magnetically soft thin structures bonded to a polymeric base-substrate layer with acrylate acetate (SUPERGLUE(copyright)) and baked. When the swellable base swells (low pH): the distance between the square magnetically soft structures enlarges resulting in less coupling between these structures. If immersed in high pH: this base shrinks as does the distance between structures resulting in a larger voltage signal.
Resonant circuitry has been used in the security tags/markers of electronic article surveillance (EAS) systems that merely detect the presence of an activated tag passing through an interrogation zone of a retail store exit. An EAS tag of this sort affixed to a retail item, which has not been deactivated by a checkout clerk indicating the item has been paid-for, sounds an alarm. For example, Appalucci et al. illustrates such a security tag having a dielectric substrate. The circuit elements of a resonant circuit 12 are formed on both principal surfaces of the substrate 14 by patterning conductive material. The security tag 10 may be deactivated by changing the resonant frequency so that the tag resonates outside of the predetermined detection frequency or by altering the circuit 12 so that it no longer resonates at all. A later patent to Appalucci et al. illustrates another such security tag having a dielectric substrate 14 onto which electrical elements are also patterned to form a resonant circuit 12. Semiconductive electrical parallel connections (bridges) made across bottom and top plates of capacitors C1 and C2 stabilize the resonant tag from electrostatic discharge but still permit the tag to be activated and deactivated. The semiconductive antistatic material comprises a polymer carrier with an ionizable salt dissolved therein to provide resistivity (103 to 108 ohms per square). The function of the antistatic material is to provide electrical drain-off bridges for the capacitors C1 and C2 to prevent damage thereto. Characteristics of the antistatic carriers include being nontoxic, substantially nonaqueous, substantially neutral in pH, capable of being applied as a thin coating or layer onto a resonant circuit using conventional coating techniques, and compatible with a release sheet and/or adhesive layer applied over the resonant tag circuit (for affixing to an item).
Alicot et al. illustrates a high frequency radio frequency identification (RFID) security tag suited for providing data about the article to which such a tag is attached. This tag has a transponder 18 comprising an RFID chip 20 and an antenna 22 positioned on surface 14 of cover 12. RFID chip 20 contains logic and memory about the article to which it will be attached. A different patent issued to Montean describes another such security marker for use in radio frequency EAS systems.
Other widely used anti-theft markers/tags (electronic article surveillance, EAS, markers) generally operate by xe2x80x9clisteningxe2x80x9d for acoustic energy emitted in response to an interrogating ac magnetic field, to sense the presence of a magnetostrictive EAS marker. Sensormatic, Inc. distributes an EAS tag (dimensions 3.8 cmxc3x971.25 cmxc3x970.04 mm) designed to operate at a fixed frequency of 58 kHz (well beyond the audible range of human hearing). These EAS tags are embedded/incorporated into articles for retail sale. Upon exiting a store, a customer walks through a pair of field coils emitting a 58 kHz magnetic field. If a tag is still in an article being carried by the customer, the tag will likewise emit a 58 kHz electromagnetic signal that can be detected using a pickup coil, which in turn may set off an audible or visual alarm. More-recently, these tags are being placed in a box-resonator, sized slightly larger than the tag, such as the tags placed within a cavity 20 of a housing (FIG. 2 of Winkler et al.).
Therefore, a versatile robust chemical sensor is needed that for obtaining information about an environmental condition (including presence, concentration, temperature, and so on of an analyte) in various diverse test samples/environments through remote query, without requiring direct electrical connection to a receiving device and without the need for specifying sensor orientation.
The new compact sensing structure, sensing apparatus, and associated method of sensing, described herein, are designed for operation within a wide range of test environments whether one-time, periodic (timed or random), or continuous on-going monitoring of a particular analyte or environment is desired. The innovative sensing structure, apparatus, and method utilize a unique resonant-circuit selective recognition technique to sense and measure minute quantities of a selected analyte in gas or liquid phase without requiring sophisticated equipment and without requiring a great deal of space. Furthermore, this new sensing apparatus can be installed/positioned and removed with relative ease and without much disruption of the test sample or test environment. The unique recognition techniques employed by the new sensing apparatus and method include: continuous emission, over a set period of time, of an interrogation field from a source (whether that source is incorporated into the receiving unit or into the sensing structure); radiating shortened pulses (timed or random) of information from the sensing structure to measure its characteristic resonant frequency, as well as radiating shortened interrogation field pulses using a source (whether that source is incorporated into the receiving unit) and listening for the sensing structures response.
If need be, the sensor may be fabricated as a micro-circuit for use in vitro, in vivo, within small-sized sealed packaging or medical test samples (e.g., a test tube), and so on. A micro-sensor can be used where space is limited, and/or it is desired that the tiny sensor be positioned further into the interior of the sample or environment being tested/monitored. And, whether or not built on a larger scale, the novel resonant-circuit sensor can be used for sensing within buildings, rooms of buildings, or other spaces through which contaminant gas passes such as a smokestack or exhaust pipe, for sensing waterways to measure metals contamination, and so on.
The new analyte sensing apparatus and associated methods were developed to utilize space more efficiently while at the same time provide sufficient chemical sensitivity. Unlike the chemical sensing units available and known EAS systems, the sensing apparatus and methods incorporate a unique sensing structure that has a resonant circuit in electrical communication with an antenna, the antenna and/or at least one component of the resonant circuit having a structural element made of a material that selectively responds to an analyte within the test environment. The structural element can be made of a wide variety of materials depending upon the type of sensing information needed and upon the selective interaction, reaction, or response that will result in a measurable change in frequency characteristics of the sensing structure. And, the structural element can be applied to, adhered to, etched to accommodate, sandwiched between, and so on, the resonant circuit component(s) and the antenna. As can be further appreciated, within the spirit and scope of the design goals and as further described herein, the selectively responsive components of the resonant circuit and the antenna associated therewith can be fabricated from micro-components or can be built on a larger scale and formed into many different shapes of many suitable materials; and several such sensors can be incorporated into an array to provide a package of sensing information about one analyte or several analytes within a test environment.
It is a primary object of this invention to provide an apparatus and associated method for detecting the presence, absence, and/or measuring the amount of an fluid analyte (whether in liquid or gas form), as well as sensing the temperature thereof. A sensing structure (sensor) is used that has an antenna in electrical communication with a resonant circuit, at least one component of which (and/or the antenna) has a structural element made of a material that selectively responds (chemically, thermally, etc.) to the analyte to provide sensing information. It is also an object of this invention that such an apparatus and method utilize electromagnetic emission measurements of the sensing structure remotely taken over a range of successive interrogation frequencies, to perform the sensing/detecting. It is also an object of this invention to provide such a sensing structure that needs no direct hard-wire connection to any field generating coil used or its emission receiving coil, but rather, is remotely located for sensing.
The advantages of providing the new sensing apparatus and associated new method, as described herein, are as follows:
(a) The invention can be used for one-time (whether disposable) operation, periodic, or continuous on-going monitoring of environmental conditions;
(b)Versatilityxe2x80x94The invention can be used for operation within a wide range of testing environments such as biomedical applications (whether in vivo or in vitro), within medical test samples, food quality/inspection (within or outside of sealed packing), monitoring of contaminants in water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring of gases/aerosols; The sensing structure can be driven (to resonate) by its own battery and timing circuit or current may be induced in the sensing structure by an EM field(s) generated using a remote coil;
(c) Simplicity of usexe2x80x94The new sensor structure can be installed/positioned and removed with relative ease and without substantial disruption of a test sample/environment;
(d) Structural design flexibilityxe2x80x94The sensor may be formed into many different shapes and may be fabricated as a micro-circuit for use where space is limited and/or the tiny sensor must be positioned further into the interior of a sample or environment being tested/monitored;
(e) Structural element design for sensing speedxe2x80x94An outer layer(s) or base substrate layer of chemically or thermally responsive material may be shaped, sized, adhered, etched, and so on, to maximize the speed at which the material responds (resulting in a change in characteristic resonant frequency of the sensing structure), allowing the sensor to provide useful information at a faster rate;
(f) Several sensors may be positioned, each at a different location within a large test environment, to sample each of the different locations, simultaneously or sequentially;
(g) Several sensors may be incorporated into an array to provide a package of sensing information about an environment, such as, analyte composition, concentration of constituent components/elements of the analyte, and temperature of the environment in which the analyte(s) is found;
(h) Receiving unit design flexibilityxe2x80x94One unit having the capacity to generate an interrogation field, as needed, as well as the capacity to receive electromagnetic waves emitted from several sensing structures, each having a characteristic operating range of resonant frequencies, positioned within the test environment may be used. This wide-band capability requires either the use of broadband antennas, such as spiral antennas, or multiple narrowband transmitting and receiving antennas; see for example the useful antenna design resource entitled xe2x80x9cAntenna Theory and Design,xe2x80x9d by Warren L. Stutzman and Gary A. Thiele, for discussions on antenna design and bandwidth.
(i) Apparatus design simplicityxe2x80x94Reducing the number and size of components required to build a sensing apparatus can reduce overall fabrication costs and add to ease of operation; for example, if the resonant circuit and its associated antenna are electrically connected to an independent, portable power source (such as a small battery and suitable timing circuit), EM waves containing valuable sensing information can be emitted therefrom without needing a separate interrogation field generation coil; and
(j) Sensor materials and size can be chosen to make one-time, disposable use economically feasible.
Briefly described, the invention includes a resonant sensing apparatus for operative arrangement within a test environment to sense an analyte. The apparatus comprises: a sensing structure having an antenna in electrical communication with a resonant circuit at least one component of which has a structural element made of a material that selectively responds to the analyte; this sensing structure will resonate at a particular characteristic resonant frequency in the presence of an interrogation electromagnetic field upon the selective response; and a receiver for remotely measuring a value for the characteristic resonant frequency. At least one component may be resistive, capacitive, and inductive in nature such that the selective response causes a change in electrical characteristics of the at least one component resulting in a change in frequency characteristics of the resonant circuit. The components of the resonant circuit can be chosen such that the characteristic resonant frequency is a function of an inductance value of one component and a capacitance value of another component. Additional such sensing structures may be incorporated into an ordered array to provide a package of sensing informationxe2x80x94each of the sensing structures designed (shape, size, material) to operate at a different characteristic resonant frequency for detection thereof.
The structural element may take the form of a myriad of different structural shapes of many suitable materials (e.g., electric dielectrics, magnetic dielectrics, chemically responsive alloys, a sorbent polymer film selected from the group consisting of a poly(isobutylene), ethylene-propylene rubber, poly(isoprene), and poly(butadiene) film, a polymer hydrogel having a plurality of microspheres reactive to electrostatic forces of subatomic particles within the analyte, a structure with an outer zeolite layer, a thin outer layer sputtered onto the antenna, etc.), depending upon the desired selective response of this element to the analyte and/or to the environment surrounding the sensor. For example, the structural element may contain a plurality of ferromagnetic elements embedded within a polymeric material located in proximity of windings (whether or not planar) of an inductor. Furthermore, the selective response of the structural element may comprise a myriad of responses such as swelling, causing relocation of these ferromagnetic elements, which in turn changes the magnetic permeability of the inductor, thus affecting an inductance value of the inductor; or an interaction with the analyte resulting in a change in material stiffness of the structural element; or interaction with the analyte causing a change in relative permittivity of a dielectric material (permittivity: ∈=∈0(permitivity in free space)*dielectric constant), thus, affecting a capacitance value of the at least one component; or a thermal response to the analyte for sensing a temperature thereof (the material being thermally-sensitive, for example, a thin outer layer bonded/adhered to one of the components of the resonant circuit or to the antenna volumetrically expands in response to a temperature change); or, if the material is a chemically receptive polymer, the selective response could comprise absorption of subatomic particulate matter from the analyte; or, if the material is a chemically receptive porous polymer, selective response can comprise interaction with the analyte causing a change in magnetic permeability of the at least one component; and so on.
The component(s) of the resonant circuit may have a myriad of structures, too. One of the components of the resonant circuit can comprise a conductive segment (of many suitable shapes and sizes), wherein at least a length of this conductive segment functions also as the antenna. And, in the event at least a part of the structural element is bonded to this length, the selective response would cause a change in electrical characteristics of the antenna. One of the components may comprise electrically-isolated first and second conductive segments (whether relatively planar, flat-plate, looped, and/or concentric) between which at least a portion of the structural element is located. The first conductive segment may be a relatively planar spiral (which also functions as an inductor for the resonant circuit) adhered to a first surface of the structural element.
The receiver can include a pick-up coil/antenna capable of measuring a plurality of successive values for electromagnetic emission intensity of the sensing structure taken over an operating range of successive interrogation frequencies; this operating range to include the characteristic resonant frequency value of the sensing structure. The resonant frequency value detected will correspond to the relative maximum of the plurality of successive values for electromagnetic emission intensity measured. The receiver""s pick-up coil/antenna can be wired in communication with a frequency analyzer. The interrogation electromagnetic field may comprise a pulse of electromagnetic energy emitted just prior to each resonant frequency value measurement taken, or could include pulses emitted, successively, at predetermined intervals. The receiving unit (especially, if intended for portable-field use) may include a battery of some sort (such as an electrochemical cell) coupled to a timing circuit allowing a transmission coil/antenna to emit a series of EM pulses. It may be desirable to couple the sensing structure""s antenna to a battery of some sort (such as an electrochemical cell) and a timing circuit allowing it to emit pulses at pre-determined intervals for remote measurement thereof by the receiver. A pre-correlation made between a series of resonant frequency values taken for the sensing structure and a corresponding series of analyte sensing values can be used for the sensing (including sensing concentration, presence/absence of the analyte, temperature, moisture content, pH, etc.). For example, a pre-correlation made between a series of resonant frequency values for the sensing structure and a corresponding series of temperature values for this particular sensing structure can be used by the apparatus of the invention for sensing a temperature.
Additionally, an on-off switch comprising a ferro-electric element, permanently located in proximity to the at least one component of the resonant circuit, may be included with the apparatus. Furthermore, at least one component of the resonant circuit may comprise a magnetizable on-off switch made of a magnetically hard element which, when activated, causes the characteristic resonant frequency to fall outside of a predetermined operating range of frequencies.
Another resonant sensing apparatus having a receiver for remote measurement, as characterized herein, includes: a sensing structure operatively arranged within a test environment comprising an antenna in electrical communication with a resonant circuit having first and second components bonded to a structural element made of a material that selectively responds to the analyte in a manner that changes the frequency characteristics of said resonant circuit; and as before, sensing structure resonates at a characteristic resonant frequency in the presence of an interrogation electromagnetic field upon the selective response. Another resonant sensing apparatus, as characterized herein, includes a sensing structure comprising an antenna in electrical communication with a resonant circuit, the antenna comprising a structural element that selectively responds to the analyte causing a change in electrical characteristics of the antenna.
Within the spirit and scope of the invention, characterizations of a novel method of sensing an analyte with a sensing structure having an antenna in electrical communication with a resonant circuit are included herein. One such method characterization comprises the steps of: applying an interrogation electromagnetic field causing the sensing structure to resonate, at least one component of the resonant circuit comprising a structural element made of a material that selectively responds to the analyte; and remotely measuring, with a receiver, a value for a characteristic resonant frequency of the sensing structure upon its resonating and the selective response. Another such characterization includes: operatively arranging the sensing structure within a test environment, the antenna to comprise a structural element that will selectively respond to the analyte causing a change in electrical characteristics of the antenna; applying an interrogation electromagnetic field causing the sensing structure to resonate at a characteristic resonant frequency upon the selective response; and remotely measuring a value for characteristic resonant frequency.
The unique additional features of the apparatus, as described above, also apply to the characterizations of the method of the invention. These distinguishing features include, but are not limited to: the resonant circuit component(s) features; the receiver""s features; the interrogation field alternatives and associated radiating/emission thereof; features of the structural element and its material; the myriad of selective responsiveness alternatives of the structural element; the remote measurement of resonant frequency values; the pre-correlation of a series of resonant frequency values taken for the sensing structure and corresponding series of analyte sensing values; the application of a known mathematical relationship(s) to find values that change after selective response; the operative arrangement of a second sensing structure (having a second antenna in electrical communication with a second resonant circuit, wherein a second structural element selectively responds to the analyte, such that a value for a second characteristic resonant frequency of this second sensing structure, upon its resonance and selective response, can be found); and so on.